While pregnant, don't try to maintain a model's figure. You are now eating for two, and you must eat accordingly. Discuss your diet with your doctor. Also, exercise is appropriate, especially during the early stages of pregnancy, as long as light to moderate. You also need to discuss this with your doctor.
Habits and addictions are hard to break, but you need to avoid substance that are dangerous to both you and your baby:
Just play it safe and discuss any questions with your doctor. Get plenty of sleep and visit your doctor regularly. Your progress throughout pregnancy needs to be monitored, so contact your doctor as soon as possible once you know you're pregnant.